In systems of the above kind the custom made shell part is usually made by some sort of rapid prototyping like SLA prototyping. Here, the obtainable precision is not high enough and the material is not strong enough to allow a conventional and reliable snap fit to be produced. Further, it is a problem that very little space is available and at the same time a reliable connection is needed, which will not inadvertently release itself if the hearing aid or audio device is accidentally dropped onto a hard surface or when the user changes the battery.
U.S. Patent Application Publication 2004/0258264 A1 an in-the-ear hearing aid is described wherein the hearing aid comprises a faceplate shaped to match spatial contours of that region of a human pinna to which the aid is designed to interface. The plate is fabricated by stereo lithography. The hearing aid additionally comprises a peripheral frame, and a socket module suitable for insertion into a human's auditory canal. The socket module is adapted to receive an electronic module comprising a microphone for receiving sound at the aid. The peripheral frame and the socket module described in the U.S. Patent Application Publication 2004/0258264 document are additional elements which add to the complexity of the hearing aid and it would be advantageous if the electronic module, the socket module and the peripheral frame were integrated into one and the same element which could be fastened into the custom made part.
Further prior art document WO 2002071794 discloses a hearing aid with a custom made shell part and a module for accommodating the electronics, which is fastened directly into the custom made part. In this document the practical problems relating to the provision of a detachable connection between a custom made shell part and a module are not addressed.